lycoming O 360 wont turn over when starting

H

henryinparadise

Filing Flight Plan
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Oct 27, 2023
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Henry
The engine would barely crank over.
Checked battery and connections. All were fine.
Jumped off a truck battery. Same result.
Jumped directly to the starter. Same result.
Installed a rebuilt started. Same result.
Jumped the new starter directly. Same result.
Prop rotates as normal.
Took out the top plugs. Prop turns over very easily.
Borescoped all cylinders. Looks perfect.
Im stumped.
Not the battery, solenoid or starter.
Its in a RV 7.
thanks for any ideas.
 
henryinparadise said:
The engine would barely crank over.
Checked battery and connections. All were fine.
Jumped off a truck battery. Same result.
Jumped directly to the starter. Same result.
Installed a rebuilt started. Same result.
Jumped the new starter directly. Same result.
Prop rotates as normal.
Took out the top plugs. Prop turns over very easily.
Borescoped all cylinders. Looks perfect.
Im stumped.
Not the battery, solenoid or starter.
Its in a RV 7.
thanks for any ideas.
Click to expand...
Is this a new problem?

If so, has anything changed/maintenance work been done under cowl?

Is there a ground strap between your engine and the airframe? If so, are the connections good?
 
What's the voltage at the starter when cranking? What's the voltage at each connection while cranking? Find where the voltage drop is and you'll find the problem. It could be on the ground side, too.

Plugs and cylinders aren't going to keep the engine from cranking.
 
Were all of these attempts thru the key switch?

Starter ground seems like the obvious choice.

Though it's possible the rebuilt starter just happened to be dead.
 
kyleb said:
Is this a new problem?

If so, has anything changed/maintenance work been done under cowl?

Is there a ground strap between your engine and the airframe? If so, are the connections good?
Click to expand...
this is a new problem. the plane has been perfect over all.
no maintenance at all for 6 months. first time cowling has been off
in 6 months.
yes there is a ground strap and all connections seem tight.
 
Dana said:
What's the voltage at the starter when cranking? What's the voltage at each connection while cranking? Find where the voltage drop is and you'll find the problem. It could be on the ground side, too.

Plugs and cylinders aren't going to keep the engine from cranking.
Click to expand...
ill check the voltage tomorrow.
 
the starter of course is bolted to the engine with a solid
connection.
i did check the voltage between the pos side of the battery and the
engine and then the tail pipe and they read the same as between the battery terminals. 13 volts.

how about if i run jumper cable from the neg side of the battery to
an engine bolt or tail pipe?
 
Lndwarrior said:
Were all of these attempts thru the key switch?

Starter ground seems like the obvious choice.

Though it's possible the rebuilt starter just happened to be dead.
Click to expand...
i ran power right to the starter with same results.
when i did that i put the ground clamp on an near
by engine bolt not the starter.
 
Please get an A&P involved before you kill yourself or your plane. Taking advice from SGOTI without all the information isn't the best approach.
 
henryinparadise said:
the ground was connected to the engine and the exhaust pipe.
Click to expand...
The ground strap needs to be connected between the engine and a common grounding point on the firewall. Ideally, the point where your battery's negative terminal is grounded.
 
have you had the battery load checked? seeing voltage is like knowing there is water in a pipe, you have no idea if there is any pressure (ie amps to crank with). sounds like your battery is on its way out and does not have enough capacity to crank it over.
 
unsafervguy said:
have you had the battery load checked? seeing voltage is like knowing there is water in a pipe, you have no idea if there is any pressure (ie amps to crank with). sounds like your battery is on its way out and does not have enough capacity to crank it over.
Click to expand...
Not the right analogy. Voltage is comparable to the pressure; amps is comparable to the amount of flow.

If there's 12V at the starter (between the big terminal and the starter case), then the starter is had or something else is making the engine hard to turn. If there's significantly less than 12V, then you gave to look for a voltage drop across each other component and connection in the circuit.
 
Dana said:
Not the right analogy. Voltage is comparable to the pressure; amps is comparable to the amount of flow.

If there's 12V at the starter (between the big terminal and the starter case), then the starter is had or something else is making the engine hard to turn. If there's significantly less than 12V, then you gave to look for a voltage drop across each other component and connection in the circuit.
Click to expand...
yes my analogy was not the best, the point i was trying to make is that when the starter is not turning, having correct voltage at the starter doesn't mean a lot. if the battery does not have the capacity, as soon as the switch is thrown that voltage drops and it cranks slow and heats up. any time i see a starter turning slow issue and it "just started happening" the first thing that should be done is charge battery on the bench properly and load test it.
 
unsafervguy said:
yes my analogy was not the best, the point i was trying to make is that when the starter is not turning, having correct voltage at the starter doesn't mean a lot. if the battery does not have the capacity, as soon as the switch is thrown that voltage drops and it cranks slow and heats up. any time i see a starter turning slow issue and it "just started happening" the first thing that should be done is charge battery on the bench properly and load test it.
Click to expand...
There won't be any voltage at the starter until the starter switch is closed.
 
Recap:
OP's used two different starters, and has jumped directly to the starter with both. The symptom is that the engine won't crank, not that it won't fire.

So: Either bad power sources (two, aircraft battery and truck battery), bad starters (two, original and rebuilt replacement), or something is causing the engine to resist turning (OP says this has also been examined with no obvious issues found).
 
A question just to eliminate any ambiguity "engine barely cranking" is synonymous with "prop is struggling to turn, or not turning, when the starter should be engaged", yes? Or am I misinterpreting how you judge a "cranking" engine?

If you bypassed the aircraft electrical system an ran leads directly to the starter from a known-good power supply (which it sounds like you did from this comment: "Jumped directly to the starter. Same result." -- and used airplane/truck batt), and the thing still failed to "crank" (aka: observation is that prop was not budging or barely moving), then wouldn't the clear conclusion be a faulty starter? Have you tried bench testing either your starter or the rebuilt one you had lying around to make sure either actually works?

FWIW, when my starter was beginning to fail earlier this year the symptoms made it look like I had a weak/failing battery. It was slow to turn the prop and seemed to just give up after 1 or 2 sluggish turns and made a groaning sound, then other times it would crank 5-6 times and get the engine started. Onlookers all thought the battery was trash (it wasn't: it was a brand new Concorde). Popped a freshly overhauled starter in there and it fired right up beautifully.
 
arrow flier and all others
thanks for your advice

the prop will rotate 1/2 to 1 revolution and that is it.

i did bench test both starters
the old one did feel & sound like a bearing going bad
the new one felt fine

the only thing that makes any sense is that both starters
are bad. the new one was supposedly rebuilt and looks
rebuilt ie: clean, oiled, etc.
the old one has 900 hrs on the engine its attached to.

what i may do today is swing by one of the 3 a&ps in my county
and see if he can give me any advice and then take the old starter to
a starter repair shop 30 miles away and see what they say.
maybe both starters.

am i correct in saying that most anything metalic on the engine
is a good source of a ground? ie, bolts, exhaust pipes, etc

why are planes so frustrating?
 
henryinparadise said:
the ground was connected to the engine and the exhaust pipe.
Click to expand...
The exhaust system is NOT a good ground for starting currents. It's fine for the tiny static currents for refuelling purposes.
kyleb said:
The ground strap needs to be connected between the engine and a common grounding point on the firewall. Ideally, the point where your battery's negative terminal is grounded.
Click to expand...
Many airplanes have a strap from the engine to a clean spot on the engine mount, which is bolted to the airframe. Those bolted connections need to be clean, too, not dirty or oily or loose or corroded.
Jim_R said:
So: Either bad power sources (two, aircraft battery and truck battery), bad starters (two, original and rebuilt replacement), or something is causing the engine to resist turning (OP says this has also been examined with no obvious issues found).
Click to expand...
Bad jumper cables, or cheap cables that are far too small. I've seen cheap jumpers made from 12-gauge wire, while the starter needs 6 or 4 gauge. Cheap jumper clamps also are made from thin stamped metal that have tiny contact points on whatever they're clamped to, and those spots cannot carry the requisite current.
 
unsafervguy said:
any time i see a starter turning slow issue and it "just started happening" the first thing that should be done is charge battery on the bench properly and load test it.
Click to expand...
No. The first thing is to get out the multimeter and start taking voltage readings. Charging the battery and load-testing it takes lots of time, while voltage measurements are quick and tell the real story. From the Skytec starter troubleshooting data:

1734379804062.png
The details and explanations are found here: https://skytec.aero/aircraft-starter-performance-issues/

One cheap little multimeter and the knowledge how to use it and interpret the readings can save many hours and dollars. Many.

Unfortunately, the knowledge is the scarce part. That's where the details in the Skytec stuff come in.

When I was about 18 I bought a Sanwa analog multimeter. 53 years later I'm still using it. It has saved me and customers and friends a great deal of money. I think I paid around $40 or $50 for it, a king's ransom for a teenager in that day. It would be ten times that now for a good-quality analog meter. But we can buy digital multimeters for $10, sometimes. There is no excuse not to buy one and learn to use it.
 
In 1977 I went to Nashville Auto Diesel college. We were taught to troubleshoot battery cable systems with volt meters. On analog meters use the 2.5vdc scale and record line drop at across every cable under load. For return ground systems that includes between ground cables and the starter housings or starter motor ground post. All of the cable voltage drops added together should be less than 1/2 Vdc.

The starter should pull the battery down to about 10 volts and the starter rolling should be above 9.5.

Hope this helps
 
@henryinparadise I used the information provided above by @Dan Thomas and others a few years ago when my battery was supposedly going bad and one A&P wanted me to replace it. Another A&P suggested the starter as the culprit.

So being cheap, I took my $20 multimeter and spent some time with the plane. It ended up being 2 things. I replaced the starter contactor first. Much improved but still not perfect. Then found a big drop in the 8” wire between the contactor and starter which was aluminum and starting to corrode, which I had someone custom make a new one and I installed it. Happy plane.

It’s fun and rewarding in an electrical geek sort of way.
 
henryinparadise said:
i ran power right to the starter with same results.
when i did that i put the ground clamp on an near
by engine bolt not the starter.
Click to expand...
If you mean the engine mount bolt that would not be a ground due to the rubber isolator.

A recent YouTuber pointed out that using the exhaust pipe as a ground might not work either.
 
thanks Dan, William and 455
You all had the same advice and ill do just that today.
I was able to talk to one of the only 3 a&ps in my county ystrdy and he
gave me the same advice.
i also got the number of a man who does nothing but repair starters
about an hour drive away in a tiny town of 200.
he was quite a character. not a big talker. he took the old starter, disassembled it, put in a new bushing, new solenoid, lots of testing,
inspecting, pronounced it "good as new" charged me $105 (cash only).
no credit cards, no checks
ill install that today
 
Dan Thomas said:
When I was about 18 I bought a Sanwa analog multimeter. 53 years later I'm still using it. It has saved me and customers and friends a great deal of money. I think I paid around $40 or $50 for it, a king's ransom for a teenager in that day. It would be ten times that now for a good-quality analog meter. But we can buy digital multimeters for $10, sometimes. There is no excuse not to buy one and learn to use it.
Click to expand...
An analog multimeter is actually better at troubleshooting these kinds of issues. Faster to react and track the fluctuations.
 
455 Bravo Uniform said:
It’s fun and rewarding in an electrical geek sort of way.
Click to expand...
Especially if it's an intermittent electrical gremlin. Pretty sure I taught the power company customer service people some new words when they were sending me unbalanced lines. They'd send a tech out and he'd measure line to ground and all is good. FINALLY convinced him to measure line to line. 232-234-253. My crane requires a step up transformer and the vfd on that doesn't like it. My press brake made a weird humming. And my CNC plasma cuts like crap. Then a few hours later, everything is balanced again.
 
AV8R_87 said:
An analog multimeter is actually better at troubleshooting these kinds of issues. Faster to react and track the fluctuations.
Click to expand...
Yes, which is why I still use that old Sanwa. I have several digital meters and some other analogs but still prefer the analogs.

The digitals are handy for capacitance, frequency, transistor checking and temperature. One has the AC ammeter clamp. I'd like to get a DC amp clamp meter. One can never have enough multimeters...:)
 
Just a stupid question, is your ground actually grounded? Possibly something got pulled loose when the cowling was off? It's one part of the circuit that I don't see tested.
 
Dan Thomas said:
I'd like to get a DC amp clamp meter.
Click to expand...
Fluke i1010, 600A AC, 1000A DC. Pair it with a Fluke 87V multimeter. Not a cheap combo, but it works well.

Dan Thomas said:
One can never have enough multimeters...:)
Click to expand...
Guilty! I order a lot of stuff from a place that offers free gifts on larger orders. Best value is the multimeter, so I never say no to another one. I give most of them away to people that need one.
 
Dan Thomas said:
One can never have enough multimeters...:)
Click to expand...
I have an analog 15kV megometer that I got for $100!! I replaced the variac transformer for $35. That machine new is $4500!!
I got lucky on that one. I haven't used it much lately, but I used to use it alot.
 
update on no starting lycoming 360

it turns over as if the battery is almost dead.

used 3 batteries. all fully charged. one out of a truck.
no help

used two starters. both recently rebuilt.
no help

checked voltage across all of the batteries while cranking. 4.5 volts
each time.

checked voltage across starter while cranking. 4.5 volts

checked continuity from battery to starter. no resistance
solid connection

checked continuity from neg side of battery to starter housing.
same. good connection.

im really stumped.
 
That cranking voltage is really bad. Something should be getting really hot. Run your hand carefully along all the cables and junctions after cranking, should be able to find a culprit. Don’t burn yourself.
 
You didn't accidentally put in a 24V starter, did you?

It would take a huge load short to pull a good battery down to 4.5V.
 
henryinparadise said:
im really stumped.
Click to expand...
You need to take a step back and start with troubleshooting the system as a whole. With a known good battery installed, disconnect your current starter, and rig up a landing light bulb in place of the starter. Now try to "start" the system and see if it will light the bulb.

And continuity is not a sign of a good connection. One strand on a cable will show continuity but not allow any amperage to pass. Same if there is a corroded/loose connection. A drop to 4.5 volts is huge and you should be able to find it provided you chase the power systematically from the battery to the starter.
 
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